Fresnel lens.



W. CHURCHILL.

FRESNEL LENS.

APPLIOATION FILED MAR.6, 1913.

Patented 001;. 21, 1913.

lllNllTlED @FFIGE.

WILLIAM CHURCHILL, 6F CQRNING, NEW YORK, ASSIGNOB, TO CQRNING GLASS-WORKS, OF CORNING, NEW YORK.

rnnsnnr. LENS.

Specification of Letters Patent.

Patented Eliot. 2f, 1533123.

Application filed March 6, 1913. Serial No. 752,425.

To all "Lo/1.0712. it may concern Be it known that I, WILLIAM Cnunomnn,a citizen of the United States, residing at Corning, in the county ofSteuben and State of New York, have invented new and useful Improvementsin Fresnel Lenses, of which the following is a specification.

In order to meet certain conditions in the use of lenses for signalingpurposes it is desirable to produce a beam of uniform intensity over arelatively wide angle. For example, in railroad service signals aresometimes necessarily located on curves, and in such. cases the spreadof beam obtainable with the ordinary semaphore lens is not sufficient tocover the entire angle through which the signal light should be visibleto afford adequate protection. On the other hand, when a Fresnel of theordinary type is employed in connection with the usual source ofillumination the concentration and corresponding magnification of lightproduced by the lens is not sufficiently great to afford a signal of therequisite brilliancy.

A lens designed and constructed according to my invention produces abeam of uniform intensity, and at the same time afl'ords muchgreater-brilliancy than can be obtainable with a Fresnel of the usualtype.

I use a lens which in general contour is cylindrical as in the case ofan ordinary Fresnel, but which differs therefrom in that its inner faceis furnished with a convex lenticular surface and with a series ofprismatic corrugations the latter condensing the light impinging on thelens in a dimension at right angles to the bounding surface of thecylinder. The outer surface of my improved lens is also furnished with aconvex lenticular surface and with a series of prismatic corrugations,but such lenticular surface and corrugations are disposed at rightangles to those on the inner face of the lens.

Furthermore, one of the faces of the lens is so constructed that itshall have a curvature and condensing power different from the curvatureand condensing power of the other face of the lens. I do not aim toproduce by means of the outer prisms the same amount of convergence asis effected by the inner prisms. If that were'done we should get aresult which would be practically the equivalent of that obtained by anordinary condenser having spherical surfaces on one or both faces, such,for example, as is usual in a lens of the so-called semaphore. type. Theprisms on the outer face of my improved lens are merely given sufficientcurvature to converge within a relatively narrow angle the beam whichwould other wise cover a much wider angle.

Referring to the drawing, Figure 1 is a perspective view of my improvedlens. Fig.

2 is a cross section of the lens on the axis A.-D. Fig. 3 is a top. viewof the lens, and illustrates the convergence of the beam by means of theprisms of the outer face. Fig. 4 is a front view of the lens.

It will be seen from Fig. 3 that, although the Fresnel lens is sodesigned as to cover a horizontal angle of 70 degrees with respect tothe source of illumination at the point A, namely the angle B-A-F, yet,by means of the converging prisms on the outer face, the light, whichotherwise would be distributed uniformly over the angle BAF, isconvergcdand condensed over the narrow angle CAE, which in this instance is oneof degrees. Accordingly within the limits of said angle CA-E, there isdouble the illumination which could be obtained in case the lens wereconstructed in the usual manner with prismatic corrugations on one faceonly, the other face being cylindrical. l have accordingly produced alens which possesses'the important characteristic of distributing thelight received over a relatively wide angle with uniform intensity, andwhich further, by means of the corrugations on the outer face, largelyincreases the intensity of the projected beam within the limits of itsspread.

While Fig. 3 affords an illustration of the convergence of a beam of 70degrees spread within an angle of 35 degrees whereby is secured doublethe intensity which a lens of the ordinary Fresnel type and similardimensions could produce, by condensing a beam of say 75 degrees ofspread into 25 degrees we can, if desired, produce a beam having threetimes the intensity of one pro duced by a similar Fresnel. It istherefore obvious that the principle herein described admits of a Widevariety of applications ac cording to special requirements.

I do not limit myself to the exact design before mentioned whereinprismatic corrugations, characteristic of the ordinary Fresnel, aredisposed upon the inner face, and a second series of prismaticcorrugations are disposed on the outer face at right angles to thefirst. This relation, if so desired, may be reversed, thereby bringingthe prisms of less curvature and condensing power upon the inner face,while the other series of prisms at right angles to the first, and ofgreater condensing power, are disposed upon the outer face of theFresnel segment. It is also obvious that such Fresnel segments may becombined, if desired, to form a cylinder of 360 degrees, the individualsegments being united by metal fittings, cement or similar means.

Having thus described my invention, I claim 1. A Fresnel lens having itsinner and outer faces each provided with a convex lenticular surface anda series of prismatic corrugations parallel thereto, the convexlenticular surface and prismatic corrugations disposed on one face ofthe lens being at right angles to those disposed upon its otherlenticular surface and a series of prismatic corrugations parallelthereto, the convex lenticular surface and prismatic corrugationsdisposed on one face of the lens being at right angles to those disposedupon its other face, and each face of the lens having differentcurvature and condensing power, substantially as set forth.

In testimony whereof I affix my signature in presence of two witnesses.

WILLIAM CHURCHILL. I

Witnesses:.

DELPHINE KEAGLE, G. WILLIS DRAKE.

